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  • Title/Summary/Keyword: Tidal Current Environment

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A Study on the Flow Characteristics around Tidal Current Turbine (조류발전용 터빈 주위의 유동 특성에 관한 연구)

  • Kim, Bu-Gi;Yang, Chang-Jo
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.18 no.6
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    • pp.610-616
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    • 2012
  • All the countries in the world is currently facing the full scale of energy-climate era currently, and making strong energy policy that will lead to green growth of the future energy resources by utilizing renewable energy as the basis of entering the advanced country becomes the goal of development that satisfies the demand for energy in 21st century. Recently, ocean energy attracted the attention along with the necessity of developing renewable energy. Ocean energy is the one of most prominent recyclable and clean resources that has not been developed yet. So, it is highly required to develop good tidal current energy conversion system in coastal area. The inflow angle that acts against tidal current turbine, seabed effect and the change of efficiency along the occurrence of cavitation were investigated through the wake flow characteristics in this study. Power coefficient degradation by seabed effect did not appear in the condition of this calculation. Efficiency degradation appeared from above 10 regarding inflow angle and power coefficient was calculated as lower by 7 % at 45. Torque and power coefficient increased as inflow velocity rose, but power coefficient degradation appeared from above 3m/s when the cavitation happened. So, it was recognized that the larger inflow angle and occurrence of cavitation become the reason for power degradation through the flow characteristics.

A Study on the Improvement of Risk Assessment Items and Index for Sunken Ship (침몰선박 위해도 평가항목 및 평가지수 개선에 관한 연구)

  • Lee, Seung-Hyun;Choi, Hyuek-Jin;Suh, Jae-Joon
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.21 no.6
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    • pp.704-711
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    • 2015
  • In this study, we have conducted a survey of AHP technique through the ocean experts to derive new items and revise assessment items and indices for risk of sunken ships based on the survey results. As a result of the survey, two new items such as accident cause and tidal current are derived. And it shows that existing items such as toxic liquid substance, remaining oil and explosive gas which were evaluated as one group are desirable to be evaluated respectively. Accordingly, we analyze the indices of the new eleven assessment items adjusted from the existing seven assessment items. As a result, the indices are ordered by toxic liquid substance, possibility of leaking, explosive gas, carrying capacity of fuel oil, sensitivity of sea environment, marine traffic environment, cause of accident, tidal current, keel clearance, ship type, and ship size. Especially, as compared with the indices of existing assessment items, the indices of sensitivity of sea environment and possibility of leaking are higher and the index of keel clearance is lower.

Marine Environmental Characteristics of Seagrass Habitat in Seomjin River Estuary (섬진강 하구역 잘피(Z. marina)서식지의 해양환경 특성)

  • Ji, Hyeong-Seok;Seo, Hee-Jeong;Kim, Myeong-Won;Lee, Moon Ock;Kim, Jongkyu
    • Journal of Ocean Engineering and Technology
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    • v.28 no.3
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    • pp.236-244
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    • 2014
  • This study considered a seagrass habitat in order to analyze the characteristics of a marine environment of seagrass located in the Seomjin river estuary, through an analysis of the distribution of the water depth, field observation, and three-dimensional numerical experiments using an EFDC model. The seagrass habitat was usually distributed at D.L(-) 0.5~0.0 m, and was hardly seen in the intertidal zone higher than that range. The distribution of the water temperature was within the range of 7.023.2C, and the seagrass was demonstrated to have a strong tolerance to changes in the water temperature. In addition, the salinity distribution was found to be 27.2~31.0 psu, with suspended solids of 32.1 mg/L, which were higher than the previous research results (Huh et al., 1998), implying that there may be a reduction in the amount of deposits caused by the suspended solids. As for the sedimentary facies, they were comprised of 62.7% sand, 19.1% silt, and 18.2% clay, indicating that the arenaceous was superior and the sedimentary facies were similar to that of Dadae Bay. According to a numerical experiment, the maximum tidal current was 75 cm/s, while the tidal residual current was 10 cm/s, confirming that it sufficiently adapted to strong tidal currents. The erosion and deposition are predicted to be less than 1.0 cm/year. Thus, it is judged that the resuspension of sediments due to tidal currents and the changes in sedimentary facies are insignificant.

Coastal Circulation and Bottom Change due to Ocean Resort Complex Development

  • Kim, Pill-Sung;Lee, Joong-Woo;Kim, Jeong-Seok
    • Journal of Navigation and Port Research
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    • v.36 no.7
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    • pp.585-590
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    • 2012
  • On the basis of the potentials for the growth of local economy and the result of investigation of the ocean space development status, an ocean resort complex was proposed at the small harbor with a parallel beach in the east coast of Korea. As the development plan needs to reclaim the noticeable amount of coastal water area together with the applied shore facilities, it is necessary to analyze their impacts. Here, it was intended to analyze the coastal environment change such as water circulation and bottom change because of the development plan. A horizontal two-dimensional numerical model was applied to represent the combined impact of wind waves and tidal currents to sediment transport in that coastal region. Based on the result of 30 days tidal current simulations considering major four tidal components of M2,S2,K1 and O1 for the upper and lower boundaries and wind field data, bottom change was discussed. Flow velocities were not changed much at outer breakwater of Yangpo harbor. Bottom was eroded by maximum 1.7m after construction but some locations such as lee side of outer breakwater and some islets near the entrance shows isolated accretions. Although it needs more field observations for bottom change in the period of construction, the numerical calculation shows that there exist small impacts near the entrance area and coastal boundaries because of the development.

Tide and Tidal Currents Around the Archipelago on the Southwestern Waters of the South Sea, Korea (한국 남서해 다도해역의 조석·조류 특성)

  • Choo, Hyo-Sang;Kim, Dong-Sun
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.19 no.6
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    • pp.582-596
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    • 2013
  • In order to estimate the tide and flow properties around the archipelago, around Dolsan, Choyak, Geogeom and Jindo which located in the southwestern waters of the south sea of Korea, tidal currents, residual flows and tidal energy dissipation were investigated by using 2-dimensional numerical model. The maximum speeds of tidal currents are small around Dolsando(31.92 cm/s) and large around Jindo(87.55 cm/s). The residual flow is fastest around Choyakdo where many channels and islands as compared with other study areas. The area around Jindo has the highest currents speed, but shows the flat movements. The margins between the maximum and the minimum dispersion rates of tidal energy in the areas are estimated and designate the order of values around Dolsando(392.6×107 erg/s), Geogeumdo(125.7×107 erg/s) and Jindo(23.1×107 erg/s) sequently. These circumstances are same as in the amplitude of M2 constituent. This means that rapid depth changes and narrow channels play an important role in tide and tidal currents energy in archipelago.

Analysis of Littoral Currents by the Coupled Hydrodynamic Model (복합해수유동 수치모형에 의한 조간대 연안류의 해석)

  • Lee, Jong-Sup;Kwon, Kyong-Hwan;Park, Il-Heum
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.20 no.2
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    • pp.247-258
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    • 2014
  • To evaluate the influence of the external force components on the littoral currents in the Gusipo beach, Jeonbuk, West Coast of Korea where a wide tidal sand flat developed, a coupled hydrodynamic model considered real time tidal currents and wave-induced currents was constructed in which the EFDC for tides and tidal currents, the SWAN for waves and the SHORECIRC for wave-induced currents were used as the hindcasting models. A series of field observations for tides, tidal currents and incident waves were carried out and especially to observe the littoral currents in the tidal sand flat, the GPS mounted and light weight drogues were used. Also wind data were collected from the adjacent weather station. To analyze the littoral current components, the numerical drogue tracking results considered real time winds, tides and waves were compared with the field drogue data. The drift speed of numerical drogues was reproduced as the range of 68.0~105.2% compared with the field data and the velocity error of main direction component showed a good result as -16.7~10.0%. As a result, in the mild slope tidal flat including wide surf zone, the tides and winds were the major affection component of the littoral currents, on the other hand, the wave-induced currents seemed the minor component when the incident wave heights were relatively small.

A Study on Precise Tide Prediction at the Nakdong River Estuary using Long-term Tidal Observation Data (장기조석관측 자료를 이용한 낙동강 하구 정밀조위 예측 연구)

  • Park, Byeong-Woo;Kim, Tae-Woo;Kang, Du Kee;Seo, Yongjae;Shin, Hyun-Suk
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.28 no.6
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    • pp.874-881
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    • 2022
  • Until 2016, before discussions on the restoration of brackish water of the Nakdong River Estuary started in earnest, the downstream water level was predicted using the data of existing tide level observatories (Busan and Gadeokdo) several kilometers away from the estuary. However, it was not easy to carry out the prediction due to the dif erence in tide level and phase. Therefore, this study was conducted to estimate tide prediction more accurately through tidal harmonic analysis using the measured water level affected by the tides in the offshore waters adjacent to the Nakdong River Estuary. As a research method, the storage status of observation data according to the period and abnormal data were checked at 10-minute intervals in the offshore sea area near the Nakdong River Estuary bank, and the observed and predicted tides were measured using TASK2000 (Tidal Analysis Software Kit) Package, a tidal harmonic analysis program. Regression analysis based on one-to-one comparison showed that the correlation between the two components was high correlation coef icient 0.9334. In predicting the tides for the current year, if possible, more accurate data can be obtained by harmonically analyzing one-year tide observation data from the previous year and performing tide prediction using the obtained harmonic constant. Based on this method, the predicted tide for 2022 was generated and it is being used in the calculation of seawater inflow for the restoration of brackish water of the Nakdong River Estuary.

Numerical Simulation of Residual Currents and tow Salinity Dispersions by Changjiang Discharge in the Yellow Sea and the East China Sea (황해 및 동중국해에서 양쯔강의 담수유입량 변동에 따른 잔차류 및 저염분 확산 수치모의)

  • Lee, Dae-In;Kim, Jong-Kyu
    • Journal of the Korean Society for Marine Environment & Energy
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    • v.10 no.2
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    • pp.67-85
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    • 2007
  • A three-dimensional hydrodynamic model with the fine grid is applied to simulate the barotropic tides, tidal currents, residual currents and salinity dispersions in the Yellow Sea and the East China Sea. Data inputs include seasonal hydrography, mean wind and river input, and oceanic tides. Computed tidal distributions of four major tides(M2,S2,K1 and O1) are presented and results are in good agreement with the observations in the domain. The model reproduces well the tidal charts. The tidal residual current is relatively strong around west coast of Korea including the Cheju Island and southern coast of China. The current by M2 has a maximum speed of 10 cm/s in the vicinity of Cheju Island with a anti-clockwise circulation in the Yellow Sea. General tendency of the current, however, is to flow eastward in the South Sea. Surface residual current simulated with M2 and with M2+S2+K1+O1 tidal forcing shows slightly different patterns in the East China Sea. The model shows that the southerly wind reduces the southward current created by freshwater discharge. In summer during high runoff(mean discharge about 50,000m3/s of Yangtze), low salinity plume-like structure(with S < 30.0 psu) extending some 160 km toward the northeast and Changjiang Diluted Water(CDW), below salinity 26 psu, was found within about 95 km. The offshore dispersion of the Changjiang outflow water is enhanced by the prevailing southerly wind. It is estimated that the inertia of the river discharge cannot exclusively reach the around sea of Cheju Island. It is noted that spatial and temporal distribution of salinity and the other materials are controlled by mixture of Changjiang discharge, prevailing wind, advection by flowing warm current and tidal current.

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A Study on the Towing Force of Heavy Loaded Barge against Strong Current (강조류에서 중량물 운반 부선의 예인력에 관한 연구)

  • Kim, Chol-Seong;Rim, Geug-Soo
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.17 no.2
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    • pp.179-185
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    • 2011
  • A marine collision accident occurred at the Jin-do water way. A barge loaded with heavy equipment of Power Generation Plant was being towed at its side by two tugs "A" and "B" from Byeg-pa harbour to the designated position to be used for power generation plant near Jin-do bridge. The Power Generation Plant was 40-meters high loaded atop the barge. When the "tugs and tow" were approaching the Jin-do the bridge, the two towing tugs lost maneuvering control of the barge and it went off-course, hit first the waterway embankment and finally struck the lower part of bridge's span and post musing the barge to capsize and sunk its cargo into the sea. The bridge also suffered damages where the top of the Plant struck At the time of the accident, there was a strong tidal current at the waterway. This paper calculates the safe towing force of barges with heavy loads when traversing in a strong tidal current situation in narrow waterway.

Estimation of Extreme Tide for Risk Analysis of Marine Salvage in the Namhae (southern sea of Korea) (한국 남해의 구난환경 위험성 분석을 위한 극치 조석 산정)

  • Lee Moon-Jin
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.12 no.1 s.24
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    • pp.33-38
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    • 2006
  • In marine salvage, extreme tide heights and tidal currents are necessary to anchor an accidental ship. In order to meet this requirement, a simple scheme was developed which yields the spatial informations on the extreme tide from the distribution of approximate highest astronomical tide heights using a relationship between extreme and highest astronomical tides at the standard port. This method is the inference method based on horizontally homogeneity of tide. This scheme was applied to estimate extreme tide heights and tidal currents in the Namhae (southern sea of Korea). The highest astronomical tide heights are computed by amplitude of four major constituents (M2, S2, K1, O1 tide). The estimated extreme tide heights are ranged from 70 to 260 cm for return period 50 years and from 80 to 270cm for return period 100 years, respectively. For return period 100 years, extreme tidal currents show value of 1.55 times as strong as those of normal state.

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